| loose cannon | |
| —n | |
| a person or thing that appears to be beyond control and is potentially a source of unintentional damage | |
| a fool or simpleton; ninny. |
| a children's mummer's parade, as on the Fourth of July, with prizes for the best costumes. |
loose cannon definition
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loose cannon
One who is uncontrolled and therefore a serious and unpredictable danger. For example, We can't trust her to talk to the press
she's a loose cannon. This metaphoric expression alludes to cannon mounted on the deck of a sailing ship, which if dislodged during combat or a storm could cause serious damage to both vessel and crew by sliding about. Its figurative use dates from the first half of the 1900s.